Static current converter with means for putting it out of function



Patented Nov. 28, 1950 CONVERTER WITH MEANS FOR PUTTING IT OUT OF STATICCURRENT FUNCTION Uno Lamm, Ludvika, Sweden, assignor to Alimanna SvenskaElektriska Aktiebolaget, Vasteras, Sweden, a corporation of SwedenApplication May 17, 1947, Serial No. 743,810 In Sweden May 25, 1946 9Claims. 1

It is known, in connection with the putting of a static currentconverter out of function, to open a valve path in parallel to saidconverter in the shape of a bypass valve, which forms a directconnection between the direct current terminals of the converter throughwhich a current may pass, which is maintained for instance by theinductance in the direct current circuit or by other direct currentsources. The purpose of the said bypass valve has then mainly beenlooked upon as an unloading of the main valves of the converter. A closeexamination has shown, however, that such an unloading is not alwaysnecessary but that it is still desirable to create a bypass valve pathin the sense that it does not contain any substantial voltageoriginating from the alternating current side. According to the presentinvention the bypass valve path is therefore created by the use of oneor more of the main valves of the converter in such a connection that nosubstantial voltage originating from the alternating current side formspart of the current path. The opening of such a bypass path mayespecially be advisable as a preparatory step to put the converterentirely out of function by other means.

In order that the arcs arising in such a bypass path shall not influencethe arc paths of the other main valves of the converter, it may beadvisable to construct the valves forming part of the bypass path withseparate cathodes, i. e. to make them of what is generally referred toas a monanodic type, which however, also comprises valve vessels havingseveral anodes of the same polarity in parallel, such as are used forinstance for high currents.

The invention is preferably applicable to twoway connected converters,because in these there are always valve paths between the direct currentterminals, which do not contain any transformer winding complicating theconnection. In this case two series-connected valves coupled to the samealternating current terminal form together the bypass path. Two valvesconnected in this way are as is known never simultaneously conducting innormal operation.

back-arcing one and that opposing thereto are blocked, they willgradually be extinguished as they obtain negative voltage, and inconnection therewith the back-current in the back-arcing valve willcease and be replaced by a current of normal direction, provided thatthere is an electromotive force in this direction.

In practice it is generally most simple in such cases, when theselection of the valves forming part of the bypass valve path depends ona just occurring disturbancefor instance a back-arcingto block all thevalves but to send at the same time an impulse releasing the blocking tothe valves, which shall serve for the bypass path. For the selection,for instance the means to be described below can be employed.

If, on the other hand, the valves serving as bypass valves are selectedbeforehand, which may for instance be the case if the operation isintended to be made without a preceding disturbance, only the othervalves are blocked, for instance by ceasing the sending of releasingimpulses to them. In some cases, all such releasing impulses aresuspended and special releas- 7 ing impulses are sent to the valvesintended to serve as bypass valves.

In inverters one of the most common disturbance is, as is known, afailure of commutation, i. e. either a failing ignition of the valve inturn to be ignited or a failing extinction of the previously burningvalve. If such a failure de-- pends on conditions outside the inverter,for instance on disturbances in the alternating current network fedthereby, it is, as a rule, arbitrary which pair of valves is selected toform the bypass path, although it is often most convenient to use theunduly burning valve and the valve opposite thereto for this purpose.The only step necessary may then be to cause the unduly burning valve tosend a releasing impulse to the opposite one, while all the other valvesare blocked. If, on the contrary, the missing commutation depends onsuch a defect in a valve or its control apparatus that the valve cannotbe blocked, it is necessary to cause this valve to continue to burn,

i. e. to form part of the bypass path. Also in this case the step justdescribed may be employed.

On the accompanying drawing, Figs. 1 and 2 show diagrammatically twoforms of the invention, one of these being applied to a back-arcingrectifier and the other on an inverter with a failure of commutation.

In both figures, two-way converters operating in 3 pulsations pro cycleare shown, the

Nova 28, 195% 25 2 U. LAMM STATIC CURRENT CONVERTER WITH MEANS FORPUTTING IT OUT OF FUNCTION Filed May 17, 1947 Q. and disconnectingswitches 39, 40 in a manner analogous to that already described for therectifier of Fig. 1.

I claim as my invention:

1. In a static current converter having a plurality of valves which arenormally alternately blocked during one part of the cycle of operationand released during another part, means responsive to an abnormaldisturbing condition likely to result in failure of operation of theconverter to release at least one of said valves during the normalblocking part of its cycle to form a by-pass valve path for saidconverter containing substantially no voltage derived from thealternating current side of the converter.

2. A device as claimed in claim 1, in which said valves have separatecathodes.

3. In a static current converter having a plurality of valves connectedin pairs in series to the same alternating current terminals which arenormally alternately blocked during one part of the cycle of operationand released during another part, means responsive to an abnormaldisturbing condition likely to result in failure of operation of theconverter to release at least two of said valves connected in seriesduring the normal blocking part of the cycle of one of said valves toform a bypass valve path for direct current.

4. A device as claimed in claim 3 in which one of said valves is aback-arcing valve.

5. A device as claimed in claim 3 in which one of said valves is one inwhich the commutation has failed.

6. In a device as claimed in claim 1, said means also blocking theremaining valves of the converter during parts of their cycles in whichthey are normally released,

7. In a static current converter having a plurality of valves, means fornormally transmitting periodic releasing impulses to said valves so thatsaid valves are normally blocked during one part of the cycle ofoperation and released during another part, means responsive to anabnormal disturbing condition likely to result in failure of operationof the converter to render said first means inoperative and to send aspecial releasing impulse to some of said valves to form a bypass valvepath.

8. In a static current converter having a, plurality of ionic valveswhich are normally blocked during one part of the cycle of operation andreleased during another part, means responsive to an abnormal disturbingcondition likely to result in failure of operation of the converter totransmit blocking impulses to all said valves and to send a specialreleasing impulse to some of said valves to form a bypass valve path.

9. In a device as claimed in claim 8, said means including biassedcurrent transformers in series with some of said valves.

UNO LAMM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,064,021 Ludwig Dec. 15, 19362,119,865 Lamm June 7, 1938 FOREIGN PATENTS Number Country Date 88,730Sweden Mar. 9, 1937 90,345 Sweden Sept. 28, 1937

